Remember to not even consider anything you read or hear concerning the 3.8 engine and the auto that went with it (2007-2011). The new Pentastar and new auto are worlds apart. No hate mail please as Iím not saying one Jeep is better than the other.

All I can tell you is that I have a JKU with hardtop and itís loaded down with heavy accessories, lifted with 35ís and 4.10s. I like to drive aggressively and it doesnít matter if Iím on the freeway and or going up hills, the new 2012 with the auto trans. is a great combo and will keep pulling until you let off the gas. I was expecting to change gears just like I had to with my í08 JKU (5.13s) but was surprised to learn there is no need to whatsoever with the 2012.

So, I do know that 4.10s work very well with the combo that you are asking about. Perhaps 4.56 are even better, I personally donít know, but some here are reporting how that combo works well for them. Itís a tough call to be sure.

I live in the foot hills of the Appalachian mountains, 37s 4.11s and the 6 speed. I'm completely satisfied. It will pull every hill in 6th gear with no issues. I have no intention of regearing for a long time

I have a2012 auto with 4:88 and 35 inch tires. Seems slight overkill to me I think 4:56. Maybe someone else will chime in

when you say slight overkill, what exactly do you mean? I am trying to figure out how changing to a higher number can be overkill in situations like this..

Quote:

Originally Posted by 1222

Remember to not even consider anything you read or hear concerning the 3.8 engine and the auto that went with it (2007-2011). The new Pentastar and new auto are worlds apart. No hate mail please as Iím not saying one Jeep is better than the other.

All I can tell you is that I have a JKU with hardtop and itís loaded down with heavy accessories, lifted with 35ís and 4.10s. I like to drive aggressively and it doesnít matter if Iím on the freeway and or going up hills, the new 2012 with the auto trans. is a great combo and will keep pulling until you let off the gas. I was expecting to change gears just like I had to with my í08 JKU (5.13s) but was surprised to learn there is no need to whatsoever with the 2012.

So, I do know that 4.10s work very well with the combo that you are asking about. Perhaps 4.56 are even better, I personally donít know, but some here are reporting how that combo works well for them. Itís a tough call to be sure.

This is great to hear, and incredibly helpful for me making a decision. I did have a 2008 wrangler sport a couple years ago with the 3.8, but it was a 6 speed manual completely stock, so I never encountered any of this before.

It is sounding like 4.10s will work good, i do drive aggressive sometimes mainly because I am used to having solid power throughout the entire powerband (i had a 335 bmw before the JKU, and my non-daily driver is a heavily modified vw gti with a large turbo etc...). Like i said before it is fine on flat ground and small hills, i only really encounter and notice the bigger tires causing problems on really steep hills and with the AC on.

Hopefully someone can chime in on the 4.56s with an auto trans in the 3.6 compared with the 4.10 and shed some light on it. Although im leaning towards 4.10s.... dumb question, i need to replace the gears in the rear AND front axles, right?

thanks a bunch for all your help

Quote:

Originally Posted by spyder6

I live in the foot hills of the Appalachian mountains, 37s 4.11s and the 6 speed. I'm completely satisfied. It will pull every hill in 6th gear with no issues. I have no intention of regearing for a long time

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Good to hear, im leaning more towards the 4.10s (assumign thats what you mean?) because it seems like people have good luck in the auto trans as well.

Don't fear the gear. If you're going to pay the money to regear get what is most optimal. IMO I'd get 4.56s

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Cool. I figured if im spending the money (or not, since im gonna try and push this over on my jeep dealership since they are the ones who took the liberty to do the mods and then sell it to me without mentioning this or even thinking about it) that I should get something lower to make it drive more aggressive on hills but I wanted to make sure that i wouldn't make a mistake with 4.10s or 4.56s etc... Like i said im still new to all this

Considering the cost of parts for both diffs is about 600, plus the labor which usually ranges from 200 an axle to 750 - I'd be genuinely surprised if the dealer doesn't tell you to **** off

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haha im not fully expecting them to pay for it all, but in all complete honesty if you were in my situation wouldn't you atleast try? I mean, if they wanted to do it right they should have put the proper gears in to begin with, especially considering the person who orders the parts and installs them owns a highly modified JKU wrangler that is done right. My jeep was the first they did this too, they are trying something new and looking to get there name out there to the public that they are doing this stuff now.

I would go with the 4.56 gears. I can tell you that even at highway speeds (70+mph and 2500 RPMs) my rubi with 4.10s and 35s will downshift even on small overpasses. I used to live up there in PA so I know what you are dealing with, and yeah, if you're going to spend the money, just go with the 4.56 choice. Just rememebr that it's going to affect your mpg everywhere else as well.

I would go with the 4.56 gears. I can tell you that even at highway speeds (70+mph and 2500 RPMs) my rubi with 4.10s and 35s will downshift even on small overpasses. I used to live up there in PA so I know what you are dealing with, and yeah, if you're going to spend the money, just go with the 4.56 choice. Just rememebr that it's going to affect your mpg everywhere else as well.

I'm glad you know what I mean with where I live, the hills can be quite big and a lot of them ... Good to hear your opinion on the 4.10s too thats helpful. so now im between 4.56s and 4.88s. Do you know anything bad about a 4.88 gear set? the only reason I ask is because they are about $70 cheaper then the 4.56 on quadratec

I have a 12 JKU auto with 35's and 3:73 gears.. I think it is honestly a personal preference on what you plan to do with it. I live in the Texas Hill Country and mine runs like a spotted *** ape.. It does downshift a little more but never struggles.. It is my DD and I wheel it at least once a month..

In my humble opinion, upgrading to a 4:10 isn't worth the cost/ benefit ratio and 4:88 begin to make other things suffer, like engine rpm. My buddy has an identical jeep to mine but has 4:88's. and I kick his arse going down the highway to the beach. In return, he has a little less trouble on climbs offroad,,, sometimes. I can also tell you he runs at about 600 rpm higher that me at 70 mph and gets about 3 mpg's less than me.. Again, it is a preference a to what YOU want, not to what other people think. I would spend that money in other items if it were me..

I'm glad you know what I mean with where I live, the hills can be quite big and a lot of them ... Good to hear your opinion on the 4.10s too thats helpful. so now im between 4.56s and 4.88s. Do you know anything bad about a 4.88 gear set? the only reason I ask is because they are about $70 cheaper then the 4.56 on quadratec

Can't say anything about the taller gears as I've never had them. I used to go hunting up in Bradford county so I have been up in those hills a bit. When I had my GMC Sonoma it used to downshift like hell on those hills so I used to just leave it in D instead of the OD. The Jeep doesn't have that option unless you shift manually and leave it in 4th.

what sucks is that it probably doesn't even need to downshift (specifically for me down here) but you really can't force it to stay in 5th.

haha im not fully expecting them to pay for it all, but in all complete honesty if you were in my situation wouldn't you atleast try? I mean, if they wanted to do it right they should have put the proper gears in to begin with...

No.

It's really more about preference, and personal taste, combined with driving habits and terrain driven. They can't setup and sell each vehicle for every new owner specifically. You can order based on your needs and wants, but you bought the Jeep, all the options were listed, and I'm guessing no one held a gun to your head while signing?

You can get a jeep with 3.21, 3.73, and 4.10 gears, in either an auto or manual set-up from the factory. Based on that, what are the proper gears???

It depends on who's driving, where they drive, and what they expect?

Many here report being quite happy with 35's and 3.73's on the new 3.6, while others say you need 4.88's. Some even have the 3.21's and don't mind.

I won't argue with anyone on their preference for gearing, but almost every setup has fans and detractors.

My guess would be that if they installed 4.88 gears @ dealership, we'd be seeing another thread by another new owner asking why their New Jeep only gets 14 MPG...

Hoss

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Something is wrong with these numbers. The 5 speed in a 2013 has a 5th gear that's 0.79. If you have 4.10's and 35" tires, at 70 mph, you should be right a little more than 2,200 RPM. 2,500 RPM should be 76 mph.